Perfectionist
Rulessort-union-types

sort-union-types

Enforce sorted TypeScript union types.

Adhering to this rule ensures that union types are consistently sorted, resulting in cleaner and more maintainable code. By promoting a standardized ordering of union types, this rule makes it easier for developers to navigate and understand the structure of type unions within the codebase.

Consistently sorted union types enhance the overall clarity and organization of your code.

Important

If you use the sort-type-constituents rule from the @typescript-eslint/eslint-plugin plugin, it is highly recommended to disable it to avoid conflicts.

Try it out 

type UserRole = 'user' | 'guest' | 'admin' | 'editor'

type ResponseStatus =
  | 'timeout'
  | 'success'
  | 'pending'
  | 'error'

type InputType =
  | 'password'
  | 'tel'
  | 'number'
  | 'text'
  | 'email'

Options

This rule accepts an options object with the following properties:

type

default: 'alphabetical'

Specifies the sorting method.

  • 'alphabetical' — Sort items alphabetically (e.g., “a” < “b” < “c”) using localeCompare.
  • 'natural' — Sort items in a natural order (e.g., “item2” < “item10”).
  • 'line-length' — Sort items by code line length (shorter lines first).
  • 'custom' — Sort items using the alphabet specified in the alphabet option.
  • 'unsorted' — Do not sort items. grouping and newlines behavior are still enforced.

order

default: 'asc'

Specifies whether to sort items in ascending or descending order.

  • 'asc' — Sort items in ascending order (A to Z, 1 to 9).
  • 'desc' — Sort items in descending order (Z to A, 9 to 1).

fallbackSort

type:

{
  type: 'alphabetical' | 'natural' | 'line-length' | 'custom' | 'unsorted'
  order?: 'asc' | 'desc'
}
default: { type: 'unsorted' }

Specifies fallback sort options for elements that are equal according to the primary sort type.

Example: enforce alphabetical sort between two elements with the same length.

{
  type: 'line-length',
  order: 'desc',
  fallbackSort: { type: 'alphabetical', order: 'asc' }
}

alphabet

default: ''

Used only when the type option is set to 'custom'. Specifies the custom alphabet for sorting.

Use the Alphabet utility class from eslint-plugin-perfectionist/alphabet to quickly generate a custom alphabet.

Example: 0123456789abcdef...

ignoreCase

default: true

Specifies whether sorting should be case-sensitive.

  • true — Ignore case when sorting alphabetically or naturally (e.g., “A” and “a” are the same).
  • false — Consider case when sorting (e.g., “a” comes before “A”).

specialCharacters

default: keep

Specifies whether to trim, remove, or keep special characters before sorting.

  • 'keep' — Keep special characters when sorting (e.g., “_a” comes before “a”).
  • 'trim' — Trim special characters when sorting alphabetically or naturally (e.g., “_a” and “a” are the same).
  • 'remove' — Remove special characters when sorting (e.g., “/a/b” and “ab” are the same).

locales

default: 'en-US'

Specifies the sorting locales. Refer To String.prototype.localeCompare() - locales.

  • string — A BCP 47 language tag (e.g. 'en', 'en-US', 'zh-CN').
  • string[] — An array of BCP 47 language tags.

partitionByComment

default: false

Enables the use of comments to separate the members of union types into logical groups. This can help in organizing and maintaining large union types by creating partitions based on comments.

  • true — All comments will be treated as delimiters, creating partitions.
  • false — Comments will not be used as delimiters.
  • RegExpPattern = string | { pattern: string; flags: string} — A regexp pattern to specify which comments should act as delimiters.
  • RegExpPattern[] — A list of regexp patterns to specify which comments should act as delimiters.
  • { block: boolean | RegExpPattern | RegExpPattern[]; line: boolean | RegExpPattern | RegExpPattern[] } — Specify which block and line comments should act as delimiters.

partitionByNewLine

default: false

When true, the rule will not sort the members of an union type if there is an empty line between them. This helps maintain the defined order of logically separated groups of members.

type CarBrand =
  // Group 1
  Fiat |
  Honda |

  // Group 2
  Ferrari |

  // Group 3
  Chevrolet |
  Ford

Each group of union types (separated by empty lines) is treated independently, and the order within each group is preserved.

newlinesBetween

type: number | 'ignore'default: 'ignore'

Specifies how to handle newlines between groups.

  • 'ignore' — Do not report errors related to newlines.
  • 0 — No newlines are allowed.
  • Any other number — Enforce this number of newlines between each group, and forbid newlines inside groups.

You can also enforce the newline behavior between two specific groups through the groups options.

See the groups option.

This option is only applicable when partitionByNewLine is false.

groups

type: Array<string | string[]>

default: []

Specifies a list of union type groups for sorting. Groups help organize types into categories, making your type definitions more readable and maintainable.

Each member will be assigned a single group specified in the groups option (or the unknown group if no match is found). The order of items in the groups option determines how groups are ordered.

Within a given group, members will be sorted according to the type, order, ignoreCase, etc. options.

Individual groups can be combined together by placing them in an array. The order of groups in that array does not matter. All members of the groups in the array will be sorted together as if they were part of a single group.

Predefined groups are characterized by a single selector.

List of selectors
  • 'conditional’ — Conditional types.
  • 'function’ — Function types.
  • 'import’ — Imported types.
  • 'intersection’ — Intersection types.
  • 'keyword’ — Keyword types.
  • 'literal’ — Literal types.
  • 'named’ — Named types.
  • 'object’ — Object types.
  • 'operator’ — Operator types.
  • 'tuple’ — Tuple types.
  • 'union’ — Union types.
  • 'nullish’ — Nullish types (null or undefined).
  • 'unknown’ — Types that don’t fit into any group entered by the user.
The unknown group

Members that don’t fit into any group specified in the groups option will be placed in the unknown group. If the unknown group is not specified in the groups option, it will automatically be added to the end of the list.

Example 1

Using all selectors:

type Example =
  // 'conditional' — Conditional types.
  | (A extends B ? C : D)
  // 'function' — Function types.
  | ((arg: T) => U)
  // 'import' — Imported types.
  | import('module').Type
  // 'intersection' — Intersection types.
  | (A & B)
  // 'keyword' — Keyword types.
  | any
  // 'literal' — Literal types.
  | 'literal'
  | 42
  // 'named' — Named types.
  | SomeType
  | AnotherType
  // 'object' — Object types.
  | { a: string; b: number; }
  // 'operator' — Operator types.
  | keyof T
  // 'tuple' — Tuple types.
  | [string, number]
  // 'union' — Union types.
  | (A | B)
  // 'nullish' — Nullish types.
  | null
  | undefined;

groups option configuration:

{
  groups: [
    'conditional',
    'function',
    'import',
    'intersection',
    'keyword',
    'literal',
    'named',
    'object',
    'operator',
    'tuple',
    'union',
    'nullish',
  ]
}

Example 2

Combine and sort intersection and union groups together:

type Example =
  | AnotherType // 'named'
  | SomeType    // 'named'
  | (A & B)     // 'intersection'
  | (A | B)     // 'union'
  | (C & D)     // 'intersection'
  | (C | D)     // 'union'
  | keyof T;    // 'unknown'

groups option configuration:

{
  groups: [
    'named',
    ['intersection', 'union'],
    'unknown',
  ]
}

Newlines between groups

You may place newlinesBetween objects between your groups to enforce the newline behavior between two specific groups.

See the newlinesBetween option.

This feature is only applicable when partitionByNewLine is false.

{
  newlinesBetween: 1,
  groups: [
    'a',
    { newlinesBetween: 0 }, // Overrides the global newlinesBetween option
    'b',
  ]
}

customGroups

type: Array<CustomGroupDefinition | CustomGroupAnyOfDefinition>

default: []

Defines custom groups to match specific object type members.

A custom group definition may follow one of the two following interfaces:

interface CustomGroupDefinition {
  groupName: string
  type?: 'alphabetical' | 'natural' | 'line-length' | 'unsorted'
  order?: 'asc' | 'desc'
  fallbackSort?: { type: string; order?: 'asc' | 'desc' }
  newlinesInside?: number
  selector?: string
  elementNamePattern?: string | string[] | { pattern: string; flags?: string } | { pattern: string; flags?: string }[]
}

An type member will match a CustomGroupDefinition group if it matches all the filters of the custom group’s definition.

or:

interface CustomGroupAnyOfDefinition {
  groupName: string
  type?: 'alphabetical' | 'natural' | 'line-length' | 'unsorted'
  order?: 'asc' | 'desc'
  fallbackSort?: { type: string; order?: 'asc' | 'desc' }
  newlinesInside?: number
  anyOf: Array<{
      selector?: string
      elementNamePattern?: string | string[] | { pattern: string; flags?: string } | { pattern: string; flags?: string }[]
  }>
}

An type member will match a CustomGroupAnyOfDefinition group if it matches all the filters of at least one of the anyOf items.

Attributes

  • groupName — The group’s name, which needs to be put in the groups option.
  • selector — Filter on the selector of the element.
  • elementNamePattern — If entered, will check that the name of the element matches the pattern entered.
  • type — Overrides the type option for that custom group. unsorted will not sort the group.
  • order — Overrides the order option for that custom group.
  • fallbackSort — Overrides the fallbackSort option for that custom group.
  • newlinesInside — Enforces a specific newline behavior between elements of the group.

Match importance

The customGroups list is ordered: The first custom group definition that matches an element will be used.

Custom groups have a higher priority than any predefined group.

Usage 

// .eslintrc.js
module.exports = {
  plugins: [
    'perfectionist',
  ],
  rules: {
    'perfectionist/sort-union-types': [
      'error',
      {
        type: 'alphabetical',
        order: 'asc',
        fallbackSort: { type: 'unsorted' },
        ignoreCase: true,
        specialCharacters: 'keep',
        partitionByComment: false,
        partitionByNewLine: false,
        newlinesBetween: 'ignore',
        groups: [],
        customGroups: [],
      },
    ],
  },
}

Version

This rule was introduced in v0.4.0.

Resources

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